Orientation coding will be studied in cat striate cortex using electrophysiolgical recordings of single neurons. In preliminary work, stimulation and data analysis techniques have been developed to delimit visual receptive fields. Upon presentation of a moving, striped pattern (termed a contour adapting field) all around the receptive field, inhibition of responsiveness to central stimulation has been demonstrated. Because of the certainty with which the receptive field was delimited and excluded from stimulation by the adapting field, as well as corroborative observations, it is extremely unlikely that this inhibition originated from known receptive field regions. An intracortical origin in arrays of orientation columns is likely. This effect is termed orientation domain inhibition; evidence has been found in some simple cells for orientation domain facilitation as well. With these two domain interactions isolated from other neural responses, their possible role in contour orientation perception will be explored. Stronger interactions among units whose optimal stimulus orientations are horizontal or vertical would implicate domain interactions in the psychophysical oblique effect. A role in orientation contrast and figural illusions would be suggested if the inhibition were a) orientation selective, b) maximal when two striped peripheral patterns formed an acute angle with each other, and c) recurrent. A role in the classic figural aftereffect and current selective adaptation aftereffects would be suggested if the inhibition persisted for many seconds following removal of the striped pattern, retained its orientation selectivity, and transferred interocularly. Exclusion of the receptive field from direct stimulation enables one to rule out habituation or fatigue as the mechanisms of the cortical adaptation. This work contributes to an understanding of higher perceptual processes in brain.